High temperature conditions impose unique material requirements. For instance, turbine engine components used in aerospace and equipment used in various energy-related fields require thermal barriers to reduce induction of heat to the metal component/equipment. Application of ceramic-based thermal barrier coatings (TBCs) to a metal/alloy substrate can facilitate use and operation at higher temperatures. However, degradation of TBCs at elevated temperatures, under thermal cycling conditions and in erosive or corrosive environments has raised concerns about the durability and reliability of such materials during use and over extended time. Spallation of ceramic-based TBCs during thermo-mechanical loading and thermal cycling has been, and remains, a key problem facing the art, particularly in the turbine industry.
Currently, the coating material most often used is yttria-stabilized zirconia (YSZ). YSZ has demonstrated adequate resistance to thermal conduction, but suffers from many drawbacks including poor phase and micro-structure stability and creep resistance, as well as high oxygen diffusivity at even moderately high temperatures. Induced stress caused by creep and bond-coat oxidation results in spallation of the YSZ coating. Accordingly, the search for alternate ceramic compositions that satisfy all the thermal, chemical, and thermo-mechanical requirements continues to be an on-going concern in the art.